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Eosinophil count (serum/plasma concentration)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of eosinophils, a type of white blood cell, in your blood. Eosinophils help fight infections and respond to allergies and inflammation.

Quick summary

["Eosinophils may rise in response to allergies, infections, or certain medical conditions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
20821-5
Short code
E coli K99 Stl Ql Aggl
Synonyms
E coli K99 Stl Ql Aggl
Category
chemistry
Sample
stool
Container
Clean container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
aggl
Specimen volume
5 g
Stability
Refrigerated: 24h, Frozen: 7d
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your doctor may recommend this test to investigate symptoms like persistent itching, skin rashes, asthma, or unexplained allergies. It can also help diagnose conditions such as parasitic infections, certain cancers, or autoimmune diseases.

What to Expect Before the Test

No special preparation is needed. You may have a simple blood draw, usually done in a doctor’s office or lab. If you’re on blood-thinning medication, let your doctor know before the test.

What the Results Mean

Elevated eosinophil levels may indicate allergic reactions, parasitic infections, or inflammatory conditions. Lower levels could suggest immune suppression or other underlying health issues. Results are interpreted by your healthcare provider based on your medical history and symptoms.

Common Conditions Linked to Eosinophil Levels

High eosinophil counts are often seen in conditions like asthma, food allergies, parasitic infections, or certain types of cancer (e.g., lymphoma). Low levels may occur in people with weakened immune systems or certain chronic illnesses.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Eosinophil Level

Frequently asked questions

How often will I need this test?
Your doctor will determine how often you need this test based on your symptoms, medical history, and treatment plan. Some people may need it only once, while others may need follow-up tests periodically.
What if my results are outside the normal range?
If your results are higher or lower than expected, your doctor will discuss them with you. They may recommend further tests, treatments, or adjustments to your current medications to address the underlying cause.
Can I eat or drink before this test?
Typically, no special diet or fasting is required for this test. However, always follow your healthcare provider’s instructions, as some tests may have specific guidelines.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy